Method of determining the specific gravity and water content of concrete aggregates



Aug. 4, 1953 H. SCHAEPERKLAUS 2,647,394 METHOD OF DETERMINING THE SPECIFIC GRAVITY AND WATER CONTENT OF CONCRETE AGGREGATES Filed Feb. 4, 1950 JNVENTOR.

!. 00/: H Semmmxmus Patented Aug. 4, 1953 orifice METHOD OF DETERMINING THE SPECIFIC GRAVITY AND WATER CONTENT OF GON- CRETE AGGREGATES I v Louis H. Schaeperklaus, Cheviot, ohio I Application February 4, 1950,- Serial N0.:142,386

3 Claims.

This invention relates to the production of concrete containing cement, water, and aggregates consisting of sand or sand and gravel or crushed rock. More particularly, the invention relates to a method of controlling the tota1 water content of a concrete so that a substantially constant ratio of water to cement may be maintained. The invention relates also to a method for determining quickly, accurately, and directly the specific gravity of the aggregates and the amount of water contained by the aggregates, without the necessity of drying said aggregates, whereby a predetermined ratio of water to cement' can be more accurately maintained in concrete mixes made at the site of a construction project regardless of any variations in the specific gravity of the supply of aggregates or the water content thereof at such site.

It is recognized by engineers and designers of concrete for various construction projects and purposes, that the amount of aggregate required in a given design of concrete is depend ent upon the specific gravity of the aggregate used, and that the strength and durability'of concrete is greatly affected by the ratio of water to cement in the concrete. It is also recognized that when a given design of concrete mix is to be used in the construction of a concrete structure, it is of prime importance to maintain the ratio of water to cement constant.

-' pile may vary greatly in different parts of the stock pile, or because of rain falling thereon, it is essentially necessary to be able to determine quickly; accurately and directly at the site, the amount of Water contained by. the aggregates,

' so that a' substantially constant ratio of water to cement may be maintainedthrough accurate control of the water which is added as such. In this manner the desired composition of a concrete mix can be accurately, maintained. However, heretofore, no practical,v simple and direct method or apparatus has been devised whereby the amounts of water anddry aggregate contained in a Wet aggregate can be accurately and quickly determined without the use of intricate devices and the solution of complex equations requiring considerable skill, all of which is tedious and time-consuming. Heretofore, the time required to; determine the amount of, water and dry aggregate in a wet, aggregate has been so great that changes in the amounts of water and dry aggregate in a given wet aggregate could take place without being detected.

An object of the invention is therefore to pro:- vide a method of quickly, accurately and'directly determining the specific gravityof an aggregate :A wet aggregate consists of a mixture of dry aggregate and water. The true mix in a concrete batch is dependent upon the water added to the mix as such, and to the amount of water and aggregate added to the mix by reason of surface water on the wet aggregates ,employed.

Since the supply of aggregate at the site of a construction project usually is in the form of a stock pile which is more or less wet, depending on the weather and rainfall thereon, the water content of the wet aggregate will vary from day to day or even more frequently. It

is therefore necessary to know the amount of' water and dry aggregates in the wet aggregate" as taken from the stock pile, so that this amount I of water may be compensated for and included as part of the total amount of water which is added as such to a mix. Since the amount of water contained in the aggregates in a stock whether surface dry or or" any degree of wet ness.

A further object of the invention is to provide a quick and accurate method for determining the Weightor volume of watercontained in a unit weight, say pounds, of wet aggregate of various specific gravities. ,A further object of the invention is to provide a quick and accurate method of. determining the weight of aggregate on a surface dry basis contained in a unit weight, say 100 pounds, of wet aggregate of various specific gravities. A further object of the invention is to provide a'quick and accurate method of determining the amount of wet aggregate that is equivalent to a unit weight, say 100 pounds, of surface dry aggregate, of various specific gravities. A fu'rther object of theinvention is to provide "*"a quick and accurate method for determining 3 vide a simple and accurate method whereby the ratio of water to cement in a given concrete mix may be quickly and accurately controlled and maintained substantially constant, even though the water content of the aggregates in a stock pile thereof may vary.

A further object of the invention is to eliminate the solution of many intricate formulae heretofore necessary to obtain any of the aforementioned factors.

A further object of the invention is to eliminate the necessity of drying the aggregate in order to determine thev water content thereof.

In accordance with my method, I determine the weight of a unit volume of the aggregates on a surface dry basis, in a stock pile provided at the site or elsewhere, where the concrete is being mixed. Since the specific gravity of surface dry aggregates in a stock pile is generally uniform throughout, I need to determine the weight W1 of a quantity of such aggregate which is surface dry, that will displacea given volume V2 of water only at the commencement of con-- crete production although check determinations may be made thereafter as often as it may be deemed necessary to catch unexpected variations in the specific gravity on a surface dry basis. I select a volume V2 whose weight is equal to KAI-l0") where K1 is a constant and n is a whole number. Thus, if K is equal to unity and 12:1, the weight of volume V2 10. If the English system of weights is used V2 is equal to 10 pounds. In practice the particular volume V2 selected is one that preferably results in a direct reading of specific gravity.

Having determined the weight of the quantity of surface dry aggregate required to displace a given volume V2 of water, I then determine the weight of a quantity of aggregate in the stock pile as is, that is required to displace the same volume V2 of water- I call this weight We (wet aggregate weight), and throughout the specification it is to be understood that the term wet aggregate means aggregate that is not surface dry. Having determined the Weights W1 and W2 and knowing volume V2, I substitute these values in a simple formula and solve for. the percentage of water in a volume V2 of the wet stock pile aggregate. From the values of W1 and W2 and unit volume V2 I can determine directly the specific gravities. of the surface dry aggregate and of the wet aggregate.

Knowing the percentage of. water, in the wet aggregate, I can compute by simple arithmetic the total amount of water in a unit weight of wet aggregate, say, per hundred pounds, and the weight of aggregate on a. surface dry basis per 100 pounds of wet. aggregate. Therefore, when a given batch of concrete is to be made, the

amount of water contained in the totalv weight of aggregate used in the batch, is subtracted from the total weight. of water that the batch requires when the aggregate is computed as surface dry, the difference being the amount of water that is added as such. In this way the ratio of water to cement in a batch of concrete can be controlled to a high degree of accuracy and the method employed for making the determinations of the water content of the aggregate makes it possible to obtain the water content value in a matter of a few minutes time so that every batch of cement can be made with. substantially the same ratio of water to cement.

A description of the apparatus and, the manner in which it is used, together with an illus- 4 tration of a method of design and control of a specified concrete mix will serve to fully explain the several features and advantages of the invention.

In the drawings I have illustrated a simple form of apparatus by which the quantity of water contained in a given weight of wet aggregate may be determined quickly, accurately and directly in the practice of my invention.

In the drawings:

Figure l is a view in elevation of a device arranged and constructed for use in practicing the methods of the invention, a portion of the device being broken away and in section;

Fig. 2 is a view in section along line II-II of igure 1;

Figs. 3 and d are views in front and side elevation, respectively, of a modified form of device;

Fig. 5 is a view of a platform scale on which the device shown in Figs. 1 and 2 is mounted for use in the practice of the methods of my invention; and

Fig. 6 is a view in section taken on line VI-VI of Fig. 1.

In practicing the method of my invention I use a gravimeter comprising a measuring device I (Figs. 1, 2, 5, 6) or a modified form I thereof such as shown in Figs. 3 and 4;, and a weighing scale 2, of any suitable type such as a platform scale, having a poise or beam 3 which is graduated decimally in the same system of units as that upon which the measuring device I or I is based. The poise of scale 2 may comprise a tare beam 3a and a net weight beam 3b.

The description of this apparatus and the manner in which it is used, together with an actual method of design and control of a specified concrete mix will serve to fully explain the several features of the invention.

The measuring device I comprises a container having a section 4 of relatively large volume V1 and a displacement volume section 5 having a measured displacement volume V2. In the side wall of section 5 I provide a sight glass or gage 5. This glass or gage is scribed with a lower mark zero (0) and an upper mark one (1.0). The displacement of water of volume V2 into section 5 is represented by the height between the 0 and 1.0 marks. The dimensions or" section 5 are so proportioned that the displacement of a volume 7V2 of water into it will provide a substantial distance between marks 0 and 1.0. A plate I behind the glass 6 is fastened along its sides to section 5. Plate 1 is placed to allow free clearance between it and the glass 6. The space be tween plate I and glass 6 is open at the top and bottom, thereby allowing free access of water to this space. The side of plate 1 toward the glass has a light color so as to make the fi) and 1.0 marks on the glass plainly visible. Plate 7 cuts down the effect of wave action of the water in section 5 and makes the sighting of the water level more accurate.

In Figs. 3 and 4 I have shown a modified device I that isv provided with substantially a square or rectangular V1 section having a sloping bottom wall I!) and a hinged side wall H.. The hinged side wall H is so constructed that it may be clamped in closed position by a clamp bar 12, that can be driven into the jaws of keepers l3 secured to the side walls adjacent to side wall H. A gasket or other suitable means may be pro-. vided to effect a watertight joint around the margin of wall II when in closed position. The

device as shown in Fig.3 and 4, may be emptied ,by merely opening side wall II, and while open ment section 5' and a glass tube gage 6a, of suit-.

able diameter. The glass gage 6a is open to the V1 section'at the bottom and is held in place at the top by a hood l5 which in turn is fastened to the side'of section 5'. The hood I5 is pierced as at Hi to allow the escape of air as water risers" The tube or gage is scribed near inthe tube. the bottom with a zero mark and a unit mark (1.0) at such a height above the zero mark that the volume between these marks corresponds to unit volume V1. When water is displaced into section from the zero mark to the 1.0 mark" the volume displaced is V2.

The gages may be calibrated as follows. Scribe the 0 mark near the bottom of the gage. Add water through section 5 until the water level is at 0. This quantity of water corresponds to volume V1. I then add a known weight of water, say pounds, and the height or level to which this added water rises in section 5 determines location of the upper mark 1.0. The known weight of added water that corresponds to the volume between the .zero and 1.0 marks, I call V2. is ready for use. While the construction of measuring devices I and I are different indetail, and other details of construction may be Having calibrated the gages the device.

made, the basic feature of the apparatus *is to have a discernable volume section V2 of a known unit or units of water, say 1 or 10 units of volume. When aggregate is added to the V1 section,

water will be displaced thereby into the V2 section. In practice, such a quantity of aggregate is added that water will be displaced to the 1.0 mark of the V2 section.

By means of the gravimeter the specific gravity of a surface dry sand or aggregate may be determined as follows: the platform of scale 2 and add water until the level thereof reaches the 0 mark on gage 6:

The slide weight on the tare beam 3a is adjusted until the scale is in balance with the tare weight, i. e., the weight of container I and of the volume V1 of water therein. Surface dry aggregate is then introduced through the top of section 5 until water from the V1 section has been displaced from the 0 mark to the 1.0 mark on' gage 6. The amount of water so displaced is volume V2 and its weight is by design, say, 10 pounds. The weight on the net weight beam 3b is then adjusted until the scale is in balance. Ifthe. net weight is 26 pounds the specific gravity of that particular sand or aggregate on a surface dry basis is 2.6.

To determine the specific gravity of the same sand or aggregate when wet and containing an unknown amount of water I repeat thefabove procedure as by adding the wet aggregate through the top of section 5 until thequantity introduced into the V1 section displaces water from the zero mark to the 1.0 markonigage 6. The scale having been balanced for tarefgjweight, I slide the net weight on beam 3b untilthe: scale is in balance. If the scale shows a netwe ight of 25 pounds the specific gravity is 2.5. ,fI h'e graduations on the wet weight, beam 3b may be so calibrated that the scale reads directlythe specific gravity as 2.60, in the case of the surface I place container l on 6 dry sand or 2.50 as in the case of the wet sand or aggregates.

In general terms, I may'designate the tare weight (weight of volume V1 of water weight of container I) as W1; the weight of volume V1 of water the weight of container l and the volume of aggregate added corresponding to V2, may be designated W2. If the aggregate added is surface dry the weight thereof is (Wz-Wi) and I designate it We.

' If the aggregate added is wet, the weight thereof is (W1Wz) and for convenience I designate this weight as Ww. v Since by design the weight of volume V2 is 10 pounds, the specific gravity of the surface dry aggregates is v Q a a V2 10 W and of the wet aggregate is To determine the per cent of water in'a quantity of wet aggregate of weight Ww, the values V2, 'Ww and We are substituted in the equation If the following values are assigned to Ww, W11, V, i; e., Ww=25 lbs., W=26' pounds, then 25-26 1 X or 0.0625 or 6.25% p The pounds of water in 25 pounds of wet sand is therefore V2-0.0625 -or 10-0.0625=0.625 lb. The weight of aggregate on a surface dry basis, in 25' pounds of aggregate containing 6.25% of water by volume, is 25-0.625=24.375 in every pounds of aggregate containing 6.25% of water by volume there is i or 2.5 lbs. of water and 97.5 lbs. ofaggregate on a surface dry basis.

The above described method of determining the quantity of water in a sample of aggregate from a stock pile thereof at the site may be performed in only a few minutes time. Therefore, the operation may be repeated as often as necessary as the stock pile is consumed or as the water content is changed by rainfall or other factors, whereby the water content of the aggregate may be determined for every batch of concrete if need be. The method need not be repeated as frequently for determining the surface dry weight of a volume of aggregate corresponding to volume V2 unless the character of the aggregate has changed,- as where the stockpile might contain aggregate from different sources of pits. Having determined the quantity of water in a given weight of wet aggregate tobe'us'ed in a batch of concrete,

pounds and V2=10 of water er 100 pounds of the wet material. In column 4 is shown the pounds of material in the surface dry state per 100 pounds of the wet-material. In column 5 is shown the pounds of wet material which would be required to produce 100, pounds of surface dry material.v In columns 6 and 7, are shown, respectively, the pounds or gallons of water per 100 pounds of the Wet material. The water content is given in both pounds and gallons because some specifications are basedon pounds of water per bag of cement, whereas, others are based on gallons of water per bag of cement. The tables can be used with either type. of specification.

Tables such as Table III may beused in the design and control of concrete mixes on the basis of the data in tables such as I and II and values of specific gravity obtained by the gravimeter.

I '(1) Dry about 30 representative pounds of sand and coarse aggregate-until all surface moisture only has-evaporated. Aggregates so dried are called surface dry, as opposed to bone dry, in that surface dry aggregates'will not absorb water internally.

(2) Set the gravimeter upon a scale which is graduated in 0.01 pound, and fill with water to the"zero mark. Set this off onthe tare beam of the scale, or offset the weight by other'means "if the scale has no tare beam.

(3) Carefully add surface dry 'fine aggregates,

3 TABLE III 1 Job Date 2 Sand-rigin F. M. 3.08 S. G. S. D. 2.60. -Lbs./c. i'. Ab. V01. 162.50B 3 Stone-Ori in v S. G. S. D. 2.70 Lbs/0. 1. Ab. Vol. 168.7511 4 Concrete Class .AOement7.25 Bags/c. y. 0490. f. Ab. Vol. lBag Sand 45%V 5 Water-4.75 GaL/Bag 34.44 GaL/c. y. 7.5 GaL/c. i. 6 Abs. Vol. 1 c. y. 27. 00 c. f. 7 Abs. Vol. Ccment=7.25 0.49 =3.55 8 Abs. Vol. Water=7. 25x4. 75-5-7. 5=4. 59 8.14

9 Abs. Vol. Aggregates Required 18. 86 c. f. d I. 10 Per 01:. Yd. Per Bag 11 Sand S. D 18.86XV' .45XB 162.50=1379 Lbs. P 12 Stone S. D 86(100-V) .55XH 168. 75=1750 Lbs. R 13 Sand Wet 0. MP 13. 79 E l02.564=14l4 Lbs. 8+7. 25=195. 0 Lbs. S 14 Stone Wet 0. 01R 17. 50 L 100.892=1766 Lbs. T-2-7. 25=243. 5 Lbs. T 15 Free Water inSand 0.01S 14.14XD 300 =4.24 Gal. 16 Free Water in Ston 0. 011 17. 66XK .107 =1.'89 Gal. 11 Total Free Water I 6.13 Gal. 18 Water to Add =34.446. 13'=28. 31 Gal; +7. 25=3. 905 Gal. W

19 250 20 300 21 102. 564 22 97. 50 23 o s. 2. es e) 24 g Water/100# Wet 107 5. 25 a Wt. Reg. for 100# S. D.. L 100.892 .8 26 Wt. S. D. per 100# Wet -Z.. 09. 115 v 1 27 1 2 a ,4' 5 6 7 as Trial Adjusted True Batch 5 5" Mix Batch Trial Batch Mix 2 ML 3 28 Oement -Bags 1 d 7 29 Water Reg -Gals 4. 76 33. 25

Water in Added 30 Sand oms Water in Added 31 one 0.01TXK 32 Water in Sand & Stone. 33 Net Water Added -W 3. 905 27. 34

34 Sand s 195 1, 305 35 Stone ..T.- 244 1, 705 36 Slumn 3" 5" 37 Remarks Harsh YieZdTrue Mix Ab. Vol. 38 Cement 7 agsX0.49 3.43 0.1. 39 Water 33. 25 al+7. 5 4. 43 c. 1'. 40 Sand S 1309 -B 162.50 8. 61 c. f. 41 Stone T- 1794 -H 168. 75 =10. 65 e. I.

42 Total 27. 12 c f To demonstrate the practice of my invention and methods and the practical use of the gravimeter and tables, I will give an illustration of the design of a specific concrete mix and a. 65

method of control of the true mix by the use of the gravimeter and the tables.

Assuming that a construction project is under way and there is cement, water and stock rock) aggregates at the site and a concrete is to be made according to specifications requiring approximately 7.25 bags of cement per cubic'yard of concrete with 45% piles of fine (sand) and coarse (pebbles or crushed of the total aggr'eg ates to 7;

through the top section 5 until the waterrises to the 1.00 mark.

(4) Balance the gravimeterand contents on the weigh beam of the scale. Assume this weight is 26.00 pounds. 1 The surface dry spe-- t l -i stem. In each case the specific gravity is quicklyand directly determined without requiring complicated setups or the solution of any equations or formulas.

I now determine the amount of water and surface drys in the wet stock piles as .follows: Proceed exactly as in (2),, (.3), and (4) of A abova but use-wetsand from thestock pile. and. assume this weight is 25.01) pounds. The specific gravity of the wet sand is then 2.50. Proceed exactly as abov using wet stone from the stockpile and assumethis weight is 26.60 pounds. Then the. Specific gravity of the wet stone is 2.66.

On Table 1, across 'SG wet sand 2.50 and on Table II 2.70 across line S G wet sand 2.66 we.

will find all factors required for designing and controlling the concrete mix specified.

These factors, by means of the gravimeter and tables, can thus be determined verytsimply and accurately, and without-the necessity. of complicated apparatus or the 'solu'tionbf' intricate equations and formulae.

Design and control of concrete mix:

These factors are given on each sheet Of"i17h tables corresponding to Table III. I-Iavingdetermined the specific gravities of the surface dry and wet aggregates, the pertinent factors required for the: design areicund' in the tables and listed in the top panelof Table III. In the center panel, the design of the is determined in absolute volume, and reduced to weights of wet aggregates and added 'wa-ter required, by use of the appropriate factors listed above.

In the lower panel the quantities are conveniently listed for making thetrialmix and any required adjustments. In cclumn. 2 are listed the theoretical mix per cuhic yard; In column 3 are listed wet aggregates and added water required per cubic/yard.

A form sheetsimilar. to. the, attached Form for Concrete Design and Control should be drawn up as record and aid in conveniently outlining the requirements of the specification, the characteristics of the aggregates to be used, and the logical sequence of the use of the factors from the tables. The line .rcferencesare to, the lines as numbered on the'form. 'Wejhave previously determined by the, use of. theggravlmfiter that he s rf d y. pecific graiiity of the. sand and .stone are, respectively, 2f.'60 and zflmandthe specific wet from, the, stock, pile are, respective y... 2.5.0; respectively, Table I, line 2.50 and 'Tablefljljfline 2.66.120, find. out necessaryfactors.

[The underlined items are taken from theita'hless] in 1,. -Enter, the name i th b. and; t ev date.

and 2160.. Thereiore. We. willfl'use,

12 Line 2.--Enter the origin of the sand, the-finismodulus; the specific gravity surface -dry='2;60. and the weight per cubic foot volu-me- -162.50-"B= Line 3.-Enter the origin of the stone; the surface dryspecific gravity='2.70- and the weight per cubic foot absolute -volume=1=68. ?5 H" Lines 1 9 to 22 and. lines 23. to 26.--En'ter trom the tables in column 1 after the appropriate titles, iactors CD-E-V for sand and- J-K-L--'Z *for the stone.

Lines 4-5.-Set out the specification mix,

Lines 7-8.-Reduce the cement and water to absolute volume, the total of which is 8.14 cu.-:it.

Line 9.-l cu. yd.=27.00 less theabso'lute vol-. umes of cement and water=18586 cu. it. which is the absolute volume of the aggregates rewired-surface dry (3. 13.).

Line .l l.--.I'he-weight of S. D. sand required l,8.86 cu. ft. V. (.45%) of sand x B (where Bis equal to 162.50 pounds per cu. ft. Ab. V01.)=1,3.79

' pounds per cubic yard.

Line 12.-The weight of S. D. stone required =18.- (-V) (H being equal to. 16.8.75. lbs.,-theweight per cu. Ab.'Vo1.) =l'l50 pounds R per cu. yd.

Line 13.-Converts the weight cf 3. D; to the weight of wet or stock nilesend mediated. =.01P E (where E=102.564 pounds, the weight or wet sand required to produce 100' pounds tot S. D. sand) =l414 pounds .of sand S. .per cubicyard. Dividing 141 i pounds by 7,225 flihe ba s of cement per cu. yd), the result is: EESStEO-pounds' of sand per bag of cement used.

Line 14.-Converts the weightoi B. De'stcne to the weight of wet or stock pile stone required; .OIRXL (where -L=l00.892, -the weight ()fi wet: stone required to produce 1002p011nd5.-S..1. stone) =l7'76 pounds T per-cu. *yd Dividing- 1776 by 7.25, the value of 2435- pounds pflstone peif. bag of cement, is :obtained.

Line 15.-'The :free water in the sand='0.0.l S (14,14) D (where D=.300 the water per 100 pounds of; wet sand)=4.24 gallons.

- Line ibil hev free water in the stone=.0lT (17.66) ("K (where K=1.0'7, the content of water i n 100 pounds of wet stone) =1.89 gallons,

Line v1,-7,.-.--'Ihe;s1um off water in the sandiand stone=.6.l3 gallons per cu. yd.

Line 18.-I'he,amount of water toj-beaddedias such isthe amour-rt of water re uired births. specification "(34.44 gaii), less the: amount; 0f; water in the sand, and stone (6.13 gal.) or 28,31. gal. Dividing 28.3'1by 7.25 we obtain the value 6.905 gal; This value iS W-"the-ameuIitofwater; required per bag.

Line 222.-Divides the form into columns. with appropriate headings.

Lines 28 to 37.--Here'are1isted elements; entering into the design and centrollcfi theaninesi.

Column 1.-Enter-'-here online 29thega1ions of water required. per :bag of cement, i. .e, 4.75. and, on. lines. 33.-3A-35. the amQun-t. of added water (.WO, sand (51%) and'stone (T),v required per bag asdetermined-ondines L2 --13-+.-l@8 Enter on line 36 the desired slump'fi in. Column. 1 :is. the one bag mix as. determined. 'ihQIIX the 18116111? fications.

Column -2.-. -The size. of the; Batch mixed on he job d pends upon the sizeci. the mixer; We will assume. anfL mixer. Since; itislsimp'ler andmore accurate to handleandcontrol-abatch basedonfull bags of cement, we -wi1l,.u se,a., 7-.bag batch. 'Therelfpre. in column ,2 enter; 7; timesthe moun s. shQwn. in column, This; is the.- That Mix Barrow-which should be run in the mixer.

For pre-job-laboratory design and trial, smaller amounts are used in the same proportions, and

inch slump instead of the desired3 inch slump, and in appearance is harsh i. e., indicating'that' proportionately more sand is required. Since the water cement ratio must be held constant, only the amounts of aggregates can be varied.

Column 3.-In order to decrease the slump and smooth out the mix, the amounts of. sand and stone, respectively, are increased'to 1435 pounds and 181-0 pounds. On line 29 is the basic water requirement i. e., 33.25 gal. On line 30 is entered the amount of water in the sand .01S D (where D= 14.35 0.300)=4.31 gal. Similarly, on line-31 is entered the amount of water in the stone .OITXK, (where K=18.10 '.l0'7)'. Thesum of these two values i. e. (6.25 gal. line 32) is subtracted from the water required (33.25-625), whichshows that 27.00 gallons are to be added as such at the mixer. This adjusted batch is .then run through the mixer, and if it is found to have a 3 inch slump and to be otherwise satisfactory, this mix is then adopted as the mix for the job.

Column 4.Since this adopted mix is to be used throughout the work, and knowing the water content of the stock pile will vary, the actual wet sand and stone quantities of the adopted mix are converted to their surface dry equivalents, to obtain a True Batch Mix for future easy control. The weight of wet sand in 100 pounds (14.35) is multiplied by the weight of dry sand per 100 pounds of wet sand (U1=97.50) and obtain 1399 pounds surface dry-line 34. Similarly, the weight of wet stone in 100 pounds (18.10) is multiplied by the weight of dry stone per 100 pounds of wet stone (Z1 99.115) and obtain 1794 pounds surface dry-line 35. Since these are surface dry quantities there is no Water in the materials added, and the amount of water required would remain at the required water cement ratio 33.25 gals.

Control of mix Column 5.If for any reason the moisture content in the aggregate being used, changes due to digging deeper into the stock pilerain, etc., we would make new tests with the gravimeter to determine new specific gravities for the Wet sand and stone, as previously described. Assume these values, respectively, as 2.42 and 2.61. These are the new values for C, E, J lines 19 and 23. New values of D and E corresponding to S. G. of 2.42 (Sheet 2.66) and of K-L corresponding to S. G. 2.61 (Sheet 2.70 of the tables) are entered on lines 20, 21, 24, 25.

Using the new values of E and L (column 5), the surface dry quantities of sand and stone of the True Batch Mix are converted to equivalent weights of wet material.

1463 pounds of sand, line 34,

and (T4 L5) =17.44 102.70=1831 pounds of stone. Also, the water constant of these quantities of sand and stone are found by multiplying these weights by the new values of D and K. (S5 D5) and (T5 K5) equal to 8.15 and 4.47, respectively, and are entered on lines 30 and 31. The sum of these water contents 12.62 (line 32) is then subtracted from the gallons of water required (33.25 gal.line 29) to obtain the new net amount of Water to be added as such=20.63 gal. (line 33). The quantities then noted in col- 14' umn 5 "(adjustment 1) are the quantities needed to maintain the True Mix values of cement water, sand and stone, with a change in water content in the aggregates, from the original de- 1 sign. In similar. manner further adjustments are made whenever a change in .water content is noted in the aggregate being used.

j i Yield Lines 38 to 42.At the bottom of the sheet are shown the equations and factors necessary to convert thequantities of the True Mix" to Absolute Volumes.- The sum of the absolute volumes is the expected yield of the batch. This should be checked occasionally against the amountof concrete deposited in certain measured parts of the forms, to detect any excessive voidsin the concrete as placed.

The same type of form can be set up for speci fications where the quantities of cement and water are given in pounds instead of bags and.

gallons. Corresponding factors for thewater as gallons.

The filling out of the chart shows that the design of concrete can be made a quick, simple and accurate operation by use of the gravimeter and the tables. The simplicity and speed with which the actual water content of the aggregate can be accurately obtained and the control calculated will make it desirable to make such control checks at more frequent intervals than has heretofore been possible and lead to the production of more uniform concrete.

Having thus described the invention as it relates to the method of determining the specific gravity, and the water content of the aggregates, the methods of designing concrete and controlling the water cement ratio, and the apparatus and tables adjunct thereto, it will be apparent that various modifications and changes in detail may be made without departing from either the spirit or the scope of the invention. Therefore, what I claim as new and desire to secure by Letters Patent is:

1. A method of determining the specific gravity of comminuted aggregate that consists in (1) weighing a container having therein a quantity of water of weight W1, (2) adding to said water, comminuted aggregate in amount to displace a unit volume of water, said unit volume being equal to K1(1'10") where K1 is a constant and n is a whole number, weighing the container, water and aggregate which displaced said volume of water, whereby the specific gravity may be determined by ubtracting the second step (2) from the first step (1) and dividing the difference by the weight of the volume V2 of water.

2. The method of determining the percentage of water contained on the surface of the particles of a unit volume of aggregate which consists in determining the following weight and volume values which, when substituted in the equation where W10: weight of wet aggregate required to displace a unit volume V2 of water where V2=K1(1-10), K1 being a constant and n a whole number, We: weight of said aggregate on a surface dry basis required to displace said unit volume V2 of water and Xzthe percent of water in a quantity of wet aggregate of volume V2, said method consisting in (1) adding to a volume of water of weight W1 an amount of wet ag regate new may be used in said equation for solving .for' X,. 5

the percent of. water in aweight-Ww. of .said:

aggregate.

3. The method of determining the percentage of water contained on the surfaces of a volume V2 of wetaggregate where- V2 is equaF-to KAI-10"); K1 being a constant and n a whole number, which consists in (1-3 weighing a: volume of waterof weight We, (2) adding surface dry aggregate tosaid water in amount sufficient to displace said'volu-me V2 of said'water, (3) weigh ing' said water with the aggregate added; sa'id weight being W2, the diffierenc'e between--Wi and W2 being We, 1) weighing another volume of water of weight W1; (5) adding said aggregate in a wet state to said volume-of water :orweight- W1- in amount sufficiem'} to displace a volume equal tosaidvolume V2, 6) weighing said water and addedwet aggregate, said weight. being WW;

whereby the. percentage. X of moisture may be determined from the equation 5 u: 'J. ni

where X is :the percentage of water in said volume V10? said. wet aggregate.

v LOUIS H. SCHAEPERKLAUS;

ketereneesicitedrinlthe file of thisv patent UNITED STATES PATENTS Number .Name Date 1,149,606 i Robb Mar. 4 1930 2,0613% :Weokerly Jan.- 12, v1937 2,090,421 Larmour Aug. 17, 1937 2 28!],61'2 Beli- Apr- 21-, 1942 2,282,027 Cum-mine June 23, 1942 V FOREIGN PATENTS Number 'Coimtry Date- 

